The determination of accurate values of the rail pressure by a rail pressure sensor (RPS) is important for the operation of a common rail injection system. The pressure in a fuel reservoir of such an injection system must be regulated and monitored, so that, for example, damage to the injection system by excessive pressure may be prevented. In addition, a high degree of accuracy is important for metering in the correct injection quantity, since this is relevant to emissions. The legislation for performing an on-board diagnosis of a motor vehicle stipulates monitoring of the RPS in the normal operating range. However, at present, the correct functioning of the RPS with regard to load decrease, short circuit or offset may only be monitored in a highly limited manner.
German Patent Application No. DE 10 2008 044 050 A1 describes a fuel system of an internal combustion engine, in which the fuel quantity injected into a combustion chamber is a function of the control duration. In addition, a pressure sensor measures the pressure in the fuel rail and provides a signal. The pressure in the fuel rail may be adjusted to a setpoint pressure with the aid of a setting device, using a signal provided by the pressure sensor. To test the fuel system, a test quantity of fuel to be injected is set, and the internal combustion engine is operated at a first setpoint pressure, and a first control duration corresponding to the test quantity of fuel to be injected, in order to provide a first operating state. In addition, a speed-dependent or torque-dependent variable characterizing the first operating state is measured. Subsequently, a second operating state is set, and a variable characterizing it is likewise measured. The two measured variables are compared to one another.
A method for operating a fuel injection system of an internal combustion engine is described in German Patent Application No. DE 10 2007 032 509 A1. In this connection, at least one operating variable of an injector, which is a function of a fuel pressure prevailing in a pressure reservoir, is evaluated in order to deduce the fuel pressure.